Table Of ContentJ. Helminthol. Soc. Wash.
64(1), 1997 pp. 157-159
Research Note
Prevalence of Larval Trematodes in Helisoma trivolvis (Gastropoda)
from a Farm Pond in Northampton County, Pennsylvania with Special
Emphasis on Echinostoma trivolvis (Trematoda) Cercariae
KATHARINE A. SCHMIDT AND BERNARD FRIED'
Department of Biology, Lafayette College, Easton, Pennsylvania 18042
ABSTRACT: Occurrence of larval trematodes and sea- 1995). This snail has been collected from a farm
sonal prevalence of Echinostoma trivolvis in Helisoma pond in Northampton County, Pennsylvania, by
trivolvis snails from a farm pond in Northampton one of us (B.F.) for more than 20 yr to obtain
County, Pennsylvania, were investigated from 24 May
larval stages of E. trivolvis for laboratory studies
to 31 October 1995. Of 1,841 H. trivolvis snails (7-20
on this echinostome. Other species of larval
mm shell diameter), 589 were infected based on snail
trematodes were also observed, but no records
isolation data. Prevalence data showed that 457
of the species, their relative abundance, or the
(24.8%) released cercariae of Echinostoma trivolvis,
52 (2.8%) released cercariae of Zygocotyle lunata, 46 seasonal prevalence of E. trivolvis were kept.
(2.5%) released an unidentified species of armatae cer- The purpose of this study was to determine
cariae, 26 (1.4%) released the psilostome cercariae of which species were present at the study site, cal-
Ribeiroia sp., 5 (0.3%) released 2 unidentified species culate the overall abundance of all species
of brevifurcate-apharyngeate cercariae, and 3 (0.2%) found, and observe the pattern of E. trivolvis
released the cystophorous cercariae of Halipegus oc-
larval prevalence in the snail population during
cidualis. The percentage increase in prevalence of E.
a 6-mo period.
trivolvis was greater than 2-fold in the July versus June
Helisoma trivolvis snails were collected biweek-
collections. Previous reports on larval trematode infec-
ly from a farm pond 4 mi north of Bath, Penn-
tions in H. trivolvis are discussed.
KEY WORDS: Helisoma trivolvis, Gastropoda, Trem- sylvania, and 1 mi northwest of Klecknersville,
atoda, Echinostoma trivolvis, seasonal prevalence, cer- Pennsylvania, at 75°27'15"West, 40°47'20"North.
cariae, larval trematodes. Snails were collected from 24 May to 31 October
1995 (x = 184 per collection; range 59-380) and
Helisoma trivolvis (Say, 1816) is a ubiquitous were taken from the perimeter of the pond, no
planorbid snail in North America and is infected more than 1.5 m from the edge. The snails were
with a variety of larval trematodes (Friesen, isolated to determine infection with larval trema-
1981). Rosen et al. (1994) reported prevalence todes within 48 hr of collection by placing them
of 3 species of digenetic trematodes, Echinos- individually in Stender dishes containing 5 ml of
toma trivolvis (Cort, 1914), Cephalogonimus artificial spring water prepared according to Ulmer
vesicaudus Nickerson, 1912, and Spirorchis (1970). Two 50-watt bulbs were placed approxi-
scripta Stunkard, 1923, in H. trivolvis at Owsley mately 30 cm from the dishes to maintain the
Fork Reservoir in Kentucky. They tested the snails at 28-29°C. Each dish was examined up to
prediction that autogenic species of trematodes 4 hr after snail isolation for cercariae. Live cer-
(those that complete their life cycles in hosts liv- cariae were examined unstained or stained with
ing almost exclusively within the pond) would 0.01% neutral red and some were also fixed in
be more prevalent than allogenic species (those cold neutral-buffered formalin and mounted in
that complete their life cycles in hosts that are glycerin jelly to aid in specific or generic identi-
not always present at the pond). They found that, fication. To approximate the number of infections
contrary to their hypothesis, the allogenic spe- missed by the isolation procedure, 20% of the iso-
cies E. trivolvis was the most prevalent species. lated negative snails were crushed and examined
Echinostoma trivolvis uses H. trivolvis as its for larval trematodes.
first and second intermediate hosts (Kanev et al., Voucher specimens have been deposited in
the University of Nebraska State Museum, Har-
1 Corresponding author (e-mail: friedb@lafvax. old W. Manter Laboratory, Lincoln, Nebraska
lafayette.edu). (HWML 39074-39079).
157
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158 JOURNAL OF THE HELMINTHOLOGICAL SOCIETY OF WASHINGTON, 64(1), JAN 1997
found a greater diversity of larval trematodes in
a single location and sharing the same snail host
than in the aforementioned study. As in Rosen
et al. (1994), E. trivolvis was the most prevalent
species in the farm pond in Northampton Coun-
ty, Pennsylvania. However, we did not observe
the midsummer decline in this species that was
reported by Rosen et al. (1994). The increased
prevalence of E. trivolvis infections from June
to July can probably be explained by the devel-
opment of infections to patency in late spring to
early summer. The decreased prevalence of E.
July August September Octobe
Month of snail collection trivolvis in the fall was possibly due to death of
Figure 1. Percentage of snails infected with infected snails and/or loss of the infection. Ro-
Echinostoma trivolvis from May to October 1995. sen et al. (1994) suspected that the decreased
The number over the bar equals the sample size for
prevalence in E. trivolvis and C. vesicaudus was
that month.
due to the entry of large numbers of uninfected
snails in the population. We have no evidence to
A total of 1,841 Helisoma trivolvis snails confirm either suggestion as the reason for the
ranging in shell diameter from 7 to 20 mm was decreased prevalence of E. trivolvis.
collected, and 7 species of larval trematodes The necropsy data on purported uninfected
were found. snails reflect the fact that some infections were
Cercarial infections in snails based on isola- not yet patent when the snails were isolated or
tion were as follows: 457 (24.8%) with the echi- that cercariae were not released on the day of
nostome cercaria, Echinostoma trivolvis; 52 isolation. Cercarial release from snails, as shown
(2.8%) with the amphistome cercaria, Zygoco- by Schmidt and Fried (1996) for E. trivolvis
tyle lunata (Diesing, 1836); 46 (2.5%) with an from H. trivolvis, did not always occur on a dai-
unidentified species of armatae cercariae; 26 ly basis.
(1.4%) with the psilostome cercaria, Ribeiroia Observations on the brevifurcate-apharyngea-
sp.; 3 (0.2%) with the cystophorous cercaria, te cercariae from the 5 snails infected with this
Halipegus occidualis Stafford, 1905; 3 (0.2%) larval type suggested the presence of 2 different
with brevifurcate-apharyngeate cercariae with schistosome-like species. The cercaria with fin-
tail finfolds; and 2 (0.1%) with brevifurcate- folds was probably a turtle blood fluke and the
apharyngeate cercariae without tail finfolds. cercaria without finfolds was possibly an avian
The percentage of infection of the most prev- or mammalian schistosome. Rosen et al. (1994)
alent trematode, E. trivolvis was calculated on a noted the presence of cercariae of the turtle
monthly basis (Fig. 1). A greater than 2-fold in- blood fluke, 5. scripta from H. trivolvis in Ken-
crease in prevalence was observed from June tucky.
(12.5%) to July (32.6%). A slight decrease in The cercaria of Ribeiroia sp. may be R. tho-
prevalence was observed in September (30.9%) masi, a species previously described as Psilos-
and October (27.1%) compared to August totnum ondatrae by Beaver (1939) from the
(37.1%). snail H. antrosum percarinatum. Previous re-
Necropsies of 250 snails that were negative ports on cercariae of Zygocotyle lunata in Hel-
based on isolation showed that 92 (36.8%) har- isoma snails include those of Willey (1936) on
bored larval trematodes. No double infection this species in H. antrosum and Fried (1970) on
was found in any snail based on both isolation this species in H. trivolvis. Halipegus occidualis
and necropsy data, probably due to the low prev- larval infections have been reported from H. an-
alence of larval trematodes other than E. trivol- ceps snails by Goater et al. (1989).
vis. We have no idea what the species of the ar-
Rosen et al. (1994) recorded the prevalence matae cercaria is. According to Schell (1985),
of Echinostoma trivolvis, Cephalogonimus ves- armatae cercariae occur in the families Plagior-
icaudus, and Spirorchis scripta from Helisoma chidae, Auridistomidae, Cephalogonimidae, Te-
trivolvis snails in a reservoir in Kentucky. We lorchiidae, and Ochetosomatidae. Rosen et al.
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SCHMIDT AND FRIED—PREVALENCE OF TREMATODES IN H. TRIVOLVIS 159
(1994) noted the presence of C. vesicaudm (Ce- ture of Selected Freshwater Invertebrates. Cana-
dian Special Publication in Fish and Aquatic Sci-
phalogonimidae) cercariae in H. trivolvis from
ences, Ottawa, Canada.
Kentucky. Acholonu (1968) reported the occur-
Goater, T. M., A. W. Shostak, and J. A. Williams.
rence of xiphidiocercariae in 4 (4.3%) of 94 H. 1989. A mark-recapture study of trematode par-
trivolvis collected in Northern Colorado. asitism in overwintered Helisoma anceps (Pul-
monata) with special reference to Halipegus oc-
Acknowledgments cidualis (Hemiuridae). Journal of Parasitology 75:
553-560.
We thank Dr. Eric Wetzel, Department of Bi- Kanev, I., B. Fried, V. Dimitrov, and V. Radev.
ology, Wabash College, Crawfordsville, Indiana, 1995. Redescription of Echinostoma trivolvis
for his advice on armatae cercariae. We thank (Cort, 1914) (Trematoda: Echinostomatidae) with
a discussion on its identity. Systematic Parasitol-
Professor Ivan Kanev, Institute of Parasitology,
ogy 32:61-70.
Bulgarian Academy of Sciences, Sofia, Bulgaria, Rosen, R. B., J. M. Ilagan, J. S. Law, M. Asuncion,
for confirming the identity of Ribeiroia sp. based M. E. Denton, and M. L. San. 1994. Seasonal
on examination of cercariae fixed in neutral-buf- prevalence of three species of digenetic trema-
todes in the snail Helisoma trivolvis at Owsley
fered formalin.
Fork Reservoir, Kentucky. Transactions of the
Kentucky Academy of Science 55:32—35.
Literature Cited
Schell, S. C. 1985. Handbook of Trematodes of North
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271. cercariae of Echinostoma trivolvis from Helisoma
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